At the vertex of the parabola the first derivative of y becomes zero. So calculate, and equate it to zero. Since the corresponding x value at the vertex is given you can find b. I hope you can do it now.

Sep 21st 2011, 04:05 PM

habibixox

Re: Finding the vertex at a given point?

wait so is it
x^2-18x+91?

Sep 21st 2011, 04:07 PM

habibixox

Re: Finding the vertex at a given point?

using the second method the derivative is
-8x + x right?
set that = 0

0= -8x + x
0= X(-8+1)
so final answer is 0?

Sep 21st 2011, 04:22 PM

habibixox

Re: Finding the vertex at a given point?

nvm b = 72 now im working on c ill get it :) i understand it...

Sep 21st 2011, 07:18 PM

Sudharaka

Re: Finding the vertex at a given point?

Quote:

Originally Posted by habibixox

using the second method the derivative is
-8x + x right?
set that = 0

0= -8x + x
0= X(-8+1)
so final answer is 0?

No.

Hope you can continue.

Sep 21st 2011, 11:29 PM

Siron

Re: Finding the vertex at a given point?

The method I was thinking about is the following.
Given is the parabola: and the vertex point with coordinates
In general we know we can directly read the coordinates of the vertex of a parabola if we convert to: where are the coordinates of the parabola.